The present invention relates to an electromagnetic fuel metering and atomizing valve for an internal combustion engine fuel supply device. Known valves of the aforementioned type substantially comprise a cylindrical supporting body having a first axial cavity housing an electromagnet, and an axial hole communicating with said cavity and housing a core and an axially-sliding anchor integral with a mobile plugging member. Said valves also comprise a nozzle secured to and projecting axially from the supporting body, and in which is formed a fuel outlet hole communicating with said axial cavity and controlled by said plugging member. This is designed to move, by virtue of an electromagnet, between a first closed position wherein it is pushed by a spring against a seat on the nozzle, thus closing the fuel outlet hole, and an open position wherein the fuel outlet hole is opened. Said valves present a duct for feeding the fuel (piped to the valve) into a chamber communicating with said fuel outlet hole. Said fuel duct usually comprises an axial hole through the core and anchor on the valve, and further passages formed between further members and said supporting body and nozzle. On said valves, therefore, fuel is fed into said chamber along a duct originating at the top end and extending along the entire axial length of the valve.
A major drawback of known valves of the aforementioned type is the formation of the fuel vapours inside the fuel duct, which results in impaired operation of the valve in terms of metering and atomizing performance. This is particularly noticeable when operating with high-temperature fuel, as when the vehicle is left in the sun for prolonged periods of time.
Moreover, the pressure at which the fuel is fed into the chamber communicating with the fuel supply hole is not strictly constant, and rarely corresponds to the set pressure. As correct operation of the valve depends on the pressure of the fuel metered at each cycle being maintained strictly constant, the fuel supply circuit to the valve presents a pressure regulator for maintaining substantially constant fuel supply pressure. In the case of exceptionally long fuel ducts, however, between the upstream portion of the valve (controlled by said pressure regulator) and the chamber communicating with the fuel outlet hole, as on known valves of the aforementioned type, the pressure inside the chamber differs from that of said upstream portion due to the resistance encountered by the fuel in the duct portion formed inside the valve. Failure of such valves to provide for strictly constant fuel pressure, corresponding to the set pressure, immediately upstream from the fuel outlet hole, invariably results, as already stated, in impaired metering and atomizing performance. On certain known valves of the aforementioned type, the chamber formed inside the valve, immediately upstream from the fuel outlet hole, is supplied with fuel through holes formed inside a portion of the nozzle close to the chamber itself.
Though providing for substantially the same pressure inside the chamber and in the upstream portion of the valve (controlled by said pressure regulator) by reducing the length of the duct connecting the same, valves of the aforementioned type fail to provide a solution to the drawbacks caused by the formation of fuel vapours. Moreover, valves of this sort featuring fuel outlet holes on the nozzle involve fairly complex machining operations, thus resulting in high manufacturing cost of the valve as a whole.